Controlling interference in a wireless communication system using a parameter upper bound based on a maximum allowable noise rise

ABSTRACT

A method and apparatus for controlling interference in a wireless communication system includes a first step of performing  500  a handoff measurement of a signal parameter for a current site and for nearby sites, and performing  502  a comparison of the signal parameters to select the nearby site having the strongest signal parameter. A next step  504  includes defining a target maximum allowable noise rise for the selected nearby site. A next step  506  includes calculating an upper bound for at least one operating parameter in the current site. A next step  508  includes determining whether a maximum for the at least one operating parameter exceeds  510  the upper bound. A next step  514  includes constraining the at least one operating parameter to no more than the upper bound if the maximum for the at least one operating parameter exceeds the upper bound.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 12/399,078, filed on Mar. 6, 2009.

FIELD OF THE INVENTION

The present invention relates generally to Orthogonal Frequency DivisionMultiple Access (OFDMA) wireless communication systems, and, inparticular, to interference control OFDMA communication systems.

BACKGROUND OF THE INVENTION

Orthogonal Frequency Division Multiple Access (OFDMA) communicationsystems have been proposed for use in Long Term Evolution (LTE) andWiMAX communication systems for transmission of data over an airinterface. In OFDMA communication systems, a frequency bandwidth issplit into multiple contiguous frequency sub-bands, or sub-carriers,that are transmitted simultaneously. A user may then be assigned one ormore of the frequency sub-bands for an exchange of user information,thereby permitting multiple users to transmit simultaneously on thedifferent sub-carriers. These sub-carriers are orthogonal to each other,and thus intra-cell interference is reduced.

To maximize the spectral efficiency, a frequency reuse factor of one hasbeen proposed for both a downlink and an uplink in OFDMA communicationsystems. With a frequency reuse factor of one, data and control channelsin one sector or cell site will likely experience interference from thesame resources being un use in other sectors or cell sites. This isespecially true for user equipment (UEs) at the edge or boundary of asector or cell site or at bad coverage locations. A user located closeto the cell site but near a sector boundary will not only support a veryhigh speed, high C/I rate into the desired sector, but will alsogenerate a very high interference noise rise into those same resourceson the adjacent sector potentially rendering those adjacent sectorresources unusable. On the other hand, implementation of a traditionalpower control scheme, wherein each UE in a sector or cell site transmitsat an uplink power that results in a same received power at an enhancedNodeB for each such UE, suffers from a low overall spectral efficiencydue to a lack of UEs that can transmit at high data rates.

One solution to the problem has been to treat UEs that are close-in tothe cell site differently than those that are located at the edge orboundary of a sector or cell site or at bad coverage locations. Currentmechanisms such as in the LTE standard use a fractional power control“alpha” parameter to generically reduce available transmit power to allclose-in users based on path loss. This reduces the problem, but doesnot eliminate the problem. In particular, this solution may not fix highinterference into adjacent sectors, but just reduce the probability ofinterference. In addition, this solution reduces power (and throughput)even to users not causing interference with the end result being the UEis forced to use less power than actually required and thus experiencesa reduced user data throughput

Therefore, a need exists for resource allocation scheme that does abetter job of managing interference into adjacent sectors or cell sitesthan the current algorithms

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is pointed out with particularity in the appended claims.However, other features of the invention will become more apparent andthe invention will be best understood by referring to the followingdetailed description in conjunction with the accompanying drawings inwhich:

FIG. 1 is a simplified block diagram of a wireless communication system,in accordance with the present invention;

FIG. 2 is a simplified call flow diagram, in accordance with the presentinvention;

FIG. 3 is an illustration of a first UE of a wireless communicationsystem, in accordance with the present invention;

FIG. 4 is an illustration of a second UE of a wireless communicationsystem, in accordance with the present invention; and

FIG. 5 illustrates a method for minimizing interference, in accordancewith the present invention.

Skilled artisans will appreciate that common but well-understoodelements that are useful or necessary in a commercially feasibleembodiment are typically not depicted or described in order tofacilitate a less obstructed view of these various embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a resource allocation scheme thatminimizes interference into adjacent sectors or cell sites. Currently,in Long Term Evolution (LTE) or Fourth Generation (4G) communicationsystems, uplink modulation schemes allow Modulation and Coding Scheme(MCS) modes requiring up to nineteen decibels of carrier-to-interferenceratio (C/I) for proper operation. When near sector or cell boundaries,this can cause high interference into adjacent sectors or cell sites.The present invention makes use of existing periodic handoffmeasurements to measure the Received Signal Strength Indication (RSSI)or C/I difference between the current sector or cell site and the nextbest sector or cell site. A target maximum allowable noise rise isdefined for the other sectors or cell sites. The sum of the RSSI or C/Idifference is added to the target max noise rise to set an upper boundfor operating a user equipment (UE), as will be detailed below. As usedherein, the term “site” can be applied equally well to either cell sitesor individual sectors within a cell site.

The communication system as described herein preferably operates inaccordance with the 4G or LTE standards, which standards specifywireless telecommunications system operating protocols, including radiosystem parameters and call processing procedures. However, those who areof ordinary skill in the art realize that communication system mayoperate in accordance with any wireless telecommunication systememploying a frequency division multiplexing scheme or a time andfrequency division multiplexing scheme, such as a 3GPP (Third GenerationPartnership Project) E-UTRA (Evolutionary UMTS Terrestrial Radio Access)standard, a 3GPP2 (Third Generation Partnership Project 2) Evolutioncommunication system such as a CDMA (Code Division Multiple Access) 2000and 1XEV-DO communication system, a Wireless Local Area Network (WLAN)communication system as described by the IEEE (Institute of Electricaland Electronics Engineers) 802.xx standards, for example, the802.11a/HiperLAN2, 802.11g, 802.16, or 802.21 standards, or any ofmultiple other proposed ultrawideband (UWB) communication systems.

FIGS. 1 and 2 illustrate wireless communication system, in accordancewith an embodiment of the present invention. The communication systemcan includes multiple user equipment (UEs) 100 (one shown), such as butnot limited to a cellular telephone, a radio telephone, a personaldigital assistant (PDA) with radio frequency (RF) capabilities, or awireless modem that provides RF access to digital terminal equipment(DTE) such as a laptop computer. The communication system can furtherincludes a radio access network (e.g. 114) that provides communicationservices to each UE 100 residing in a coverage area, such as a cell or asector, of the radio access network via an air interface, e.g. 108, 123.The radio access network includes a transceiver, such as an enhancedNodeB (eNB) or a Base Transceiver Station (BTS), in wirelesscommunication with each UE 100 and further includes a networkcontroller, such as a Radio Network Controller (RNC), Base StationController (BSC), coupled to the transceiver. Air interface 110comprises a downlink and an uplink (e.g. 108, 123). Each of the downlinkand uplink comprises multiple physical communication channels, includingat least one signaling channel and at least one traffic channel.

The transceiver and controller each includes a respective processor,such as one or more microprocessors, microcontrollers, digital signalprocessors (DSPs), combinations thereof or such other devices known tothose having ordinary skill in the art. The particularoperations/functions of processors, and respectively thus of thetransceiver and controller, are determined by an execution of softwareinstructions and routines that are stored in a respective at least onememory device, as are known in the art, associated with the processor,such as random access memory (RAM), dynamic random access memory (DRAM),and/or read only memory (ROM) or equivalents thereof, that store dataand programs that may be executed by the corresponding processor.

UE 100 includes a processor 104, such as one or more microprocessors,microcontrollers, digital signal processors (DSPs), combinations thereofor such other devices known to those having ordinary skill in the art.The particular operations/functions of processor 104, and respectivelythus of UE 100, is determined by an execution of software instructionsand routines that are stored in a respective at least one memory deviceassociated with the processor, such as random access memory (RAM),dynamic random access memory (DRAM), and/or read only memory (ROM) orequivalents thereof as are known in the art, that store data andprograms that may be executed by the corresponding processor. The UEalso has the processor coupled to a transmitter 102 and a receiver 106for communicating over the air interface with the radio access network.

The UE 100 is under the control of enhanced NodeB (eNB) A. The processor104 of the UE 100 will direct the receiver 102 to perform periodichandoff measurements 202 of signals 108, 110, 112 from its own sector'seNB 114 and that of neighboring eNBs 116, 118. Although only twoneighboring eNBs are shown in this example, there can be many more toreport. The processor 104 of the UE 100 will direct the transmitter 102to report 124 these handoff metrics (e.g. RSSI or C/I difference) to thescheduler 120 through its serving eNB 114. Optionally, the scheduler canreceive a report 204 from its neighbor eNBs 116 and 118 detailing whichresources the eNBs will be using via Inter-Cell InterferenceCommunications (ICIC), for example. A processor of the scheduler 120then computes a constraint 206 on an allowable MCS and/or uplink powerlimit (C/I) for the UE 100 using the measured handoff metrics, apredefined allowable noise rise in nearby sectors, and optionally theICIC information which gives resource usage in adjacent sites. Aselected MCS/power limit is then scheduled 122 for the UE 100 throughthe eNB 114, which the UE 100 can then use 208 for its uplinkcommunications.

The constraint computation 206 used by the scheduler 120 includes adifference comparison between the handoff metrics of the UE's own sectoreNB (presumably the strongest signal) and the next strongest signal of anearby eNB. This difference is then added to the allowed noise rise forthe nearby eNB, which defines an upper limit for uplink power for the UEwhich in turn limits the modulation mode and rate combination of the UE.The scheduler 120 can then schedule 122 a selected MCS for the UE thatuses a C/I power level that is less than or equal to this upper limit.In this way, the UE should not generate a noise rise in the nextstrongest sector that exceeds the allowed noise rise when it uses 208the selected MCS for its uplink communications in the desired sector.Optionally, the constraint computation 206 can utilize any ICICinformation 204 about whether the resources in the next sector are evenin use. If the targeted resources in the next sector are not in use theninterference in that sector is not an issue, and the selected MCS willnot be constrained. If the resource is not in use in the secondstrongest cell, the constraint computation 206 can optionally be madeagainst the next strongest sector in order to continue looking forinterference constraints. If the next strongest sector is also not inuse, comparisons will continue to be made against all the neighbors inthe handoff measurement report until either the list is exhausted, inwhich case there is no limitations on the UE power, or until a givencomparison shows that there is or is not a power limitation on the UE.

It should be noted that in the example here, the scheduler performs thatconstraint computation. However, it should be recognized that theconstraint computation could be performed in any network entity. Moreparticularly, the functionality described herein as being performed bythe scheduler may be implemented in a base station transceiver orcontroller or may be distributed among the transceiver and controller,and more particularly may be implemented with or in software programsand instructions stored in a memory device of the transceiver orcontroller and executed by the respective processor of the transceiveror controller. In addition, one of ordinary skill in the art realizesthat the embodiments of the present invention alternatively may beimplemented in hardware, for example, integrated circuits (ICs),application specific integrated circuits (ASICs), and the like, such asASICs implemented in one or more of the transceiver and controller.Based on the present disclosure, one skilled in the art will be readilycapable of producing and implementing such software and/or hardwarewithout undo experimentation.

FIG. 3 shows a first operating condition addressed by the presentinvention, wherein the UE 100 is located near the center of sector A,close-in to the middle of the cell site. In the 4G communication system,this UE 100 is capable of utilizing a maximum reverse (uplink) MCS rate(at 19 dB C/I) into the eNB controlling the sector (A) serving the UE.In this geographic position in sector A, the UE 100 will performperiodic RSSI or C/I handoff measurements of its own sector and that ofneighboring sites. In this example, the UE 100 measures −60 dBm, −81dBm, and −83 dBm for sectors A, B, and C, respectively. In this case,the next strongest signal of −81 dBm comes from sector B. Doing acomparison betweens the serving sector (A) and the next best sector (B)results in a 21 dB difference (−60 dBm−(−81 dBm)=21 dB). If it isdetermined, for example, that no more than 5 dB of noise rise into nextbest sector B is acceptable, the UE can then use up to 5+21, or 26 dB,uplink C/I for its selected MCS rate before exceeding 5 dB noise rise inthe next sector. Since the maximum MCS rate needs only 19 dB C/I, the UEneed not be power or rate constrained. As a result, the UE 100 can usecenter-of-beam geometry (i.e., handoff information shows the next bestsector is 21 dB down) to maintain full power and highest uplink datarates. Unlike the prior art, which would use an “alpha” parameter toblindly back off power for the UE 100, based only on knowledge of a lowpath loss to the eNB, without regard to whether the UE is an interferer,the present invention provides higher throughput for this case.

FIG. 4 shows a second operating condition addressed by the presentinvention, wherein the UE 100 is now located near a sector boundarybetween sectors A and B, but still close-in to the cell site. As before,in the 4G communication system, this UE 100 is capable of producing amaximum reverse (uplink) MCS rate (at 19 dB C/I) into the enhanced NodeB(eNB) controlling the sector (A) serving the UE. In this geographicposition in sector A, the UE 100 will perform periodic RSSI or C/Ihandoff measurements of its own sector and that of neighboring sites. Inthis example, the UE 100 measures −60 dBm, −83 dBm, and −63 dBm forsectors A, B, and C, respectively. In this case, the next strongestsignal of −63 dBm comes from sector C. Doing a comparison betweens theserving sector (A) and the next best sector (C) results in a 3 dBdifference (−60 dBm−(−63 dBm)=3 dB). Again, if it is determined, forexample, that no more than 5 dB of noise rise into next best sector C isacceptable, the UE can then only use up to 5+3, or 8 dB, uplink C/I forits selected MCS rate before exceeding 5 dB noise rise in the nextsector. As a result, the UE 100 is constrained to use a MCS modulationand rate format that is limited to 8 dB C/I, and can not use the maximumMCS rate that operates at 19 dB C/I. Here it should be noted that havinga UE near a sector boundary has the potential of producing very highnoise rise into sector C uplink resources. The prior art would use an“alpha” parameter to blindly back off power for UE, but not enough tomitigate the problem, still causing interference in sector C. Incontrast, the present invention provides more accurate inferenceprotection.

In an optional embodiment, if it were known that the resources in nextsector were not in use (i.e. there are no communications in sector C tointerfere with), the present invention can allow the UE 100 to use themaximum MCS rate and full power anyway. To determine whether an adjacentsector/cell is in use, existing inter-cell communication techniquescould be used, such as ICIC.

It should be noted that the present invention is not limited to theclose-in UE scenarios described above, but is also applicable to UEsanywhere with the sector/site. Also, although the above embodiments aredrawn towards the prevention of a UE causing uplink interference in anearby sector of cell site, the present invention also envisions anembodiment for the downlink case, wherein the present invention could beapplied using UE handoff measurements and sector/site differences topredict forward link interference from other sectors to this specific UEon the forward link. In this embodiment, the present invention canpredict other sector/cell forward link interference to each UE, and canreduce downlink power and modulation format (MCS) in an adjacent sectorto meet the forward link maximum interference criterion as describedabove for the uplink case.

Referring to FIG. 5, another embodiment of the present inventionencompasses a method 10 for controlling uplink interference in awireless communication system. The method includes a first step 500 ofperforming a handoff measurement of a signal parameter for a currentsite and for nearby sites. Preferably, the signal parameter is areceived signal strength indication (RSSI) measurement or acarrier-to-interference ratio (C/I) measurement. This step also includesa step 502 of performing a comparison of the signal parameters to selectthe nearby site having the strongest signal parameter relative to thecurrent site by computing a difference between the signal parametermeasurements of the current site and the selected nearby siteOptionally, if the resource is not in use in the second strongest cell,the computing can be made against the next strongest sector in order tocontinue looking for interference constraints. If the next strongestsector is also not in use, comparisons will continue to be made againstall the neighbors in the handoff measurement report until either theneighbor list is exhausted, in which case there is no limitations on theUE power, or until a given comparison shows that there is or is not apower limitation on the UE.

A next step 504 includes defining a target maximum allowable noise risefor the selected nearby site. Each site can have its own maximum noiserise target, or many sites can share the same maximum noise rise target.These targets can be defined dynamically to reflect changing channelconditions.

A next step 506 includes calculating an upper bound for at least oneuplink operating parameter in the current site by summing the differencewith the target maximum allowable noise rise to set the upper bound.Preferably, the at least one uplink operating parameter includesmodulation and coding scheme (MCS) rate and/or an associatedcarrier-to-interference ratio (C/I) needed at the eNB receiverassociated with the reception of that MCS. The upper bound can berecalculated periodically by repeating steps 500-506 such as when newhandoff measurement reports are received

Another step 508 includes determining a maximum for the at least oneuplink operating parameter. This can be defined by the network whenscheduling resources. For example, the 4G communication system ispresently capable of utilizing a maximum reverse (uplink) MCS rate at 19dB C/I. This step also includes a step 510 of determining whether amaximum for the at least one uplink operating parameter exceeds theupper bound. If the maximum for the at least one uplink operatingparameter does not exceeds the upper bound, then there is no constrainton the at least one operating parameter, and the method then proceeds518 with the continuation of scheduling. Otherwise, the method continueson to the next step (512 if included, or 514). This step can optionallyinclude a step 512 of determining if the selected nearby site is in use.If it is determined that the selected nearby site is not in use, thenthere is no constraint on the at least one operating parameter, and themethod then proceeds 518 with the continuation of scheduling. Otherwise,the method continues on to the next step 514. Optionally, if theselected nearby site is not in use the determining step can instead usethe next best site to check for power constraints. This is an iterativeprocess depending on how many sites are in the handoff measurementreport. If none of the other sites have resources in use, the algorithmmay exhaust the entire list and end up with no power constraints.

A next step 514 includes constraining the at least one uplink operatingparameter to no more than the upper bound if the maximum for the atleast one uplink operating parameter exceeds the upper bound.Optionally, if it is known if the selected nearby site is in use (fromstep 512), this step also includes constraining the at least one uplinkoperating parameter only if the selected nearby site is in use.

The method then proceeds 518 with the continuation of scheduling.

Advantageously, the measurements and calculations provided by thepresent invention allow for better adjacent sector interferencemanagement, and allows higher UE throughput under low interferenceconditions than is available under the prior art.

The sequences and methods shown and described herein can be carried outin a different order than those described. The particular sequences,functions, and operations depicted in the drawings are merelyillustrative of one or more embodiments of the invention, and otherimplementations will be apparent to those of ordinary skill in the art.The drawings are intended to illustrate various implementations of theinvention that can be understood and appropriately carried out by thoseof ordinary skill in the art. Any arrangement, which is calculated toachieve the same purpose, may be substituted for the specificembodiments shown.

The invention can be implemented in any suitable form includinghardware, software, firmware or any combination of these. The inventionmay optionally be implemented partly as computer software running on oneor more data processors and/or digital signal processors. The elementsand components of an embodiment of the invention may be physically,functionally and logically implemented in any suitable way. Indeed thefunctionality may be implemented in a single unit, in a plurality ofunits or as part of other functional units. As such, the invention maybe implemented in a single unit or may be physically and functionallydistributed between different units and processors.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term comprising does not exclude the presence ofother elements or steps.

Furthermore, although individually listed, a plurality of means,elements or method steps may be implemented by e.g. a single unit orprocessor. Additionally, although individual features may be included indifferent claims, these may possibly be advantageously combined, and theinclusion in different claims does not imply that a combination offeatures is not feasible and/or advantageous. Also the inclusion of afeature in one category of claims does not imply a limitation to thiscategory but rather indicates that the feature is equally applicable toother claim categories as appropriate.

Furthermore, the order of features in the claims do not imply anyspecific order in which the features must be worked and in particularthe order of individual steps in a method claim does not imply that thesteps must be performed in this order. Rather, the steps may beperformed in any suitable order. In addition, singular references do notexclude a plurality. Thus references to “a”, “an”, “first”, “second” etcdo not preclude a plurality.

What is claimed is:
 1. A method for controlling interference in a wireless communication system, the method comprising the steps of: performing a handoff measurement of a signal parameter for a current site and for nearby sites, and performing a comparison of the signal parameters to select the nearby site having the strongest signal parameter relative to the current site by computing a difference between the signal parameter measurements of the current site and the selected nearby site; defining a target maximum allowable noise rise for the selected nearby site; calculating an upper bound for at least one operating parameter in the current site by summing the difference with the target maximum allowable noise rise to set the upper bound; determining whether a maximum for the at least one operating parameter exceeds the upper bound; and constraining the at least one operating parameter to no more than the upper bound if the maximum for the at least one operating parameter exceeds the upper bound; wherein the determining step also includes determining if the selected nearby site is in use; and wherein the constraining step also includes constraining the at least one operating parameter only if the selected nearby site is in use.
 2. The method of claim 1 wherein if the selected nearby site is not in use, a next strongest site is selected, and if the next strongest site is also not in use, repeating this step iteratively until the list of nearby sites in the handoff measurements is exhausted.
 3. The method of claim 1 wherein the signal parameter is received signal strength indication.
 4. The method of claim 1 wherein the signal parameter is a carrier-to-interference ratio.
 5. The method of claim 1 wherein the calculating step includes summing the difference with the target maximum allowable noise rise to set the upper bound.
 6. The method of claim 1 wherein if the selected nearby site is not in use, a difference is computed with a next strongest site, and if the next strongest site is also not in use, repeating this step iteratively until the list of nearby sites in the handoff measurements is exhausted.
 7. The method of claim 1 wherein the at least one operating parameter includes a modulation and coding scheme rate.
 8. The method of claim 1 wherein the at least one operating parameter includes a carrier-to-interference ratio.
 9. The method of claim 1 wherein the at least one operating parameter is at least one uplink operating parameter. 